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Can I input a voltage lower than specified output voltage to operate?

Latest Updated:05/01/2009

Question:

May I input a voltage lower than the specified output voltage to operate the circuit using a voltage lower than the specified output voltage with a 3-termina regulator?

Answer:

Although, as the VO vs. VIN characteristics indicate, the output voltage tends to decrease if the input voltage is lowered, stable operation is not guaranteed. Please input a voltage higher than the sum of the output voltage VO and the dropout voltage VDIF.
To operate the circuit using a voltage lower than the output voltage rating, you can add a constant voltage circuit that uses a Zener diode. The temperature coefficient of the RD series is not suitable for using the diode as a voltage reference diode, but, if the value shown in the characteristics graph is acceptable, it is recommended to use it.
For details about the constant voltage circuit, see the beginning of the Zener diode application circuit example in Semiconductor product types.
Suitable Products
CMOS Operational Amplifiers
Bipolar Operational Amplifiers
3 Terminal Regulators